The purpose of this project is to implement a Stack ADT in the two most common ways, an array and a linked list.
Your Stack implementation will be used to do sound manipulation, namely reversing a sound clip. This process, called “backmasking,” was used by musicians including the Beatles, Jimi Hendrix and Ozzy Ozbourne, although it seems to have fallen out of favor in recent years.
You will write a program that reads a sound file in the .dat format (explained below), and writes another .dat sound file which is the reverse of the first. We provide you with a class Reverse whose main method reads in a .dat sound file, puts the sounds values on a stack, pops them off in reverse order, and puts these reversed values in a new .dat sound file. We’ve also provided you with a DStack interface, which defines a stack that holds double values. Your first job is to look over these files and become familiar with them.
You need to provide two stack implementations, one using an array and the other using a linked list. They should be called ArrayStack and ListStack, respectively. They should implement the interface DStack, which we provide to you. Once you provide these implementations, Reverse should work and create backwards sound files. It shouldn’t take more than a page or two of code to provide the implementation. Your array implementation should hold around a million elements. You may assume that the array won’t fill completely (although we’ll discuss what happens in that case in the writeup questions). Both ArrayStack and ListStack should throw an EmptyStackException if pop() or peek() is called when the stack is empty. To use EmptyStackException, add the following line to your file:
The Reverse program takes 3 arguments. The first is the word array or list, and specifies which implementation to use. The next two are the input and output .dat file names (you need to include the .dat extension). Running the program will depend on your system; from a command line it will look something like the following.
java Reverse list in.dat out.dat
In an IDE there is usually a dialog for setting program parameters which contains a field for the program arguments.
Read the section on Digital Sound to learn how to create a .dat file. To get you started, we’ve created a .dat file here.
For details on what to turn in for this assignment and how, read the section on Logistics. For a quick reminder of how interfaces work in Java, see Java Reminder.
In addition, answer the following questions and provide the answer in your writeup.
Going Above and Beyond
The following list of suggestions are meant for you to try if you finish the requirements early. Recall that any extra-credit points you earn for these are kept separate from your assignment score and will be used to adjust your grade at the end of the quarter, as detailed in the course grading policy.
Logistics for Project 1
It may be useful for you to create some short .dat files by hand to aid testing.
Electronic turnin should be done via the online dropbox linked at the top of this page. Note that you should not turn in either Reverse.java or DStack.java. This means you shouldn’t change them, either–your code must work with the original, unmodified versions.
Your extra credit may include a modifed Reverse.java, but because you’ve included it in a separate directory we’ll be able to compile & grade your regular assignment without touching your extra credit. If you don’t segregate your extra credit you may not receive credit for it.
How Digital Sound Works
We will view sound as a continuous function of time from the positive real numbers (time) to the interval [-1.0, 1.0] (amplitude). Since a computer can’t “hold” a function defined on the reals, we have to approximate the function. We do this by measuring (or “sampling “) the sound several thousand times per second.
This process is called “Analog to Digital Conversion”, or ADC. The number of times per second the sound is sampled is called the sample rate and is measured in Hertz. For example, CDs are recorded at 44100 samples per second, or 44.1kHz. Wait a minute! Is this the right class? I thought this was CSE326.
The only sound file format you need to know about is the .dat format described below. You don’t even have to know very much about that either, as we’re giving you the code that reads and writes that format. In order to play sounds you produce, you need a way to convert the .dat file into a format that common media players (Windows Media Player, winamp, RealPlayer, etc.) understand. We’ll describe one way to do it below; however, you’re free to use any converter you can find.
sox is a UNIX command-line utility whose name stands for “SOund eXchange”. It allows you to convert between many different sound formats including .wav, .au, etc. In particular, sox allows you to convert to and from .dat sound files. .dat files are useful because they are human-readable, text-based, sound files. Note that you will need to perform this conversion to answer one of the writeup questions.
There is a windows version of
The general strategy for using
That’s all there is to it!
The .dat File Format
The .dat file format starts with one line describing the sample rate of the sound file. This line is required. The rest of the file is composed of two columns of numbers. The first column consists of the time (measured in seconds) when the sample was recorded, and the second column contains the value of the sample, between -1.0 and 1.0. This is the beginning of a sample .dat file. Notice that the numbers in the first column increase by 1/44100 each step. This is because the sample rate is 44.1kHz.
Here is the same file, a little deeper on:
Note that for this assignment, you shouldn’t have to deal much with the .dat file yourself, as the provided Reverse.java does all the lifting for you. All you have to do is implement the stacks. We are explaining the format because it will be helpful for you if you want to write a short file by hand to run, to verify if your program works.
For this assignment you will need to instantiate an interface, DStack, in two different ways. The DStack interface defines a simple stack:
An actual interface includes comments, including a description of how
The ListStack class should be defined similarly. You should include appropriate comments as needed. In particular, each file should begin with a JavaDoc comment that describes the class in the file, and includes your name and other identifying information.